There has been an increasing emphasis on reducing power usage generally. This emphasis extends to reducing electrical power usage, as from the alternating-current power mains. The recent introduction of all-electric or electrically-chargeable gas-electric hybrid automobiles has brought into focus the limitations of the power mains.
One of the little-appreciated aspects of power mains consumption lies in the ubiquitous battery-powered accessory charger, which is used to charge battery-operated appliances such as cell phones from the power mains. Many such battery-operated appliances exist, including battery-operated tools such as drills and saws, and personal grooming devices such as battery-powered toothbrushes.
A salient aspect of the use of such chargers for battery-operated appliances is that the appliances are removed from the charger for portable use. Often the charger remains in place and connected to the power mains when the appliance is removed for portable use. The term “connected” or “coupled” as used herein means “electrically connected” unless mechanical connection is clearly set forth.
Many such battery chargers use isolation transformers to protect the user of the charger from any chance of coming into contact with a power main. The transformers also provide an ancillary benefit, in that, by proper selection of the turns ratio of the primary and secondary windings, the secondary-side alternating voltage can be reduced to a range generally commensurate with the voltage of the battery or battery pack of the appliance.
It should be noted that the terms “between,” “across,” and other terms such as “parallel” have meanings in an electrical context which differ from their meanings in the field of mechanics or in ordinary parlance. More particularly, the term “between” in the context of signal or electrical flow relating to two separate devices, apparatuses or entities does not relate to physical location, but instead refers to the identities of the source and destination of the flow. Thus, flow of signal “between” A and B refers to source and destination, and the flow itself may be by way of a path which is nowhere physically located between the locations of A and B. The term “between” can also define the end points of the electrical field extending “across” or to points of differing voltage or potential, and the electrical conductors making the connection need not necessarily lie physically between the terminals of the source. Similarly, the term “parallel” in an electrical context can mean, for digital signals, the simultaneous generation on separate signal or conductive paths of plural individual signals, which taken together constitute the entire signal. For the case of current, the term “parallel” means that the flow of a current is divided to flow in a plurality of separated conductors, all of which are physically connected together at disparate, spatially separated locations, so that the current travels from one such location to the other by plural paths, which need not be physically parallel. In addition, discussions of circuits necessarily describe one element at a time, as language is understood in serial time. Consequently, a description of two interconnected elements may describe them as being in “series” or in “parallel,” which will be true for the two elements as initially described. However, further description of the circuit may implicate other interconnected devices, which when connected to the first two devices may result in current flows which contradict the “series” or “parallel” description of the original two devices. This is an unfortunate result of the limitations of language, and all descriptions herein should be understood in that context.